This invention relates to methods and apparatus for ridding wood chips, particularly imported wood chips, of pathogens such as insects, nematodes and fungi. More particularly, the invention pertains to such methods and apparatus employing hot water for pasteurization and for transport of the wood chips from a vessel, for example a ship, and an air circulation system to prevent escapement of pathogens.
Imported wood fiber of any sort and imported wood chips in particular, hereinafter referred to as "comminuted wood," pose a health threat to domestic plant species in potentially carrying pathogens from a site of origin to a site of delivery. Typically, poisonous chemicals such as aluminum phosphide or methyl bromide have been used for fumigation of imported wood fiber such as wood chips. However, such treatment chemicals cannot penetrate wood chips or large containers adequately within reasonable time. In addition, poisons are expensive to apply and must be handled and disposed of with utmost care. In addition, methyl bromide has been implicated by the Environmental Protection Agency in contributing to ozone depletion and its use is controversial. There is, generally, a conflict between the ability of a poison to function and to be harmless to the natural environment.
Attempts to employ a non-toxic and environmentally compatible agent for exterminating insects include utilizing an inert freezing liquid, such as liquid nitrogen, as proposed for example in Tallon, U.S. Pat. No. 5,165,199. However, the method of Tallon is employed for relatively small areas and volumes, as liquid nitrogen can be prohibitively expensive in large quantities. Moreover, liquid nitrogen must generally be kept away from structures or articles that it is desired should not become brittle in view of stresses placed thereon. In addition, a freezing agent may not be effective against some pathogens, such as eggs, spores and seeds.
Pasteurization has long been used to treat food products, particularly milk products, and it has even been proposed in Roth et al., U.S. Pat. No. 5,372,149 to pasteurize snuff. In the particular process of Roth, it is proposed to cook snuff in a steam jacketed vessel with stirring plows to bring the snuff into contact with the heated walls.
While pasteurization has been employed in articles for human ingestion, it has apparently not been proposed to employ such a process in the treatment of wood chips. In particular, it has not been previously known how to apply such a process in the treatment of imported wood chips, which are generally delivered to a delivery site in extremely large quantities in a ship's cargo hold, where it is desirable to prevent the escape of pathogens to the local environment.
Accordingly, there is a need for a novel and improved method and apparatus for wood chip pasteurization that pasteurizes wood chips prior to exposure to the local atmosphere and which is relatively inexpensive, non-toxic and environmentally compatible.